Function match

src/compute-engine/cost-function.ts:89–108

(
      xPow: Expression,
      ePow: Expression
    )

 *
 * To change the cost function used by the engine, set the
 * `ce.costFunction` property of the engine or pass a custom cost function
 * to the `simplify` function.
 *
 */
/**
 * Price a `Power(base, exp)`. Extracted so the alias heads that canonicalize
 * to a Power (`Square`, `Exp`) price identically to the canonical form — the
 * cost function must not depend on which representation it is handed.
 *
 * The base is mostly ignored so that `2q^2` beats `2qq`, except when the base
 * is a `Negate` (so `(-x)^n` is not cheaper than `-x^n`) or a `Multiply` (so
 * `(ab)^n` is not artificially cheaper than the distributed `a^n b^n`).
 */
function powerCost(base: Expression, exp: Expression): number {
  const expCost = costFunction(exp);
  // Count a negated base too. This used to be a flat `expCost + 4`, which
  // discarded everything under the sign — the same defect as the removed
  // `Negate(Power(...))` shortcut, just on the other side. Once `Power` began
  // counting its base it became load-bearing: `(-sin x)^2` scored 5 against
  // `sin(x)^2` at 12, so the gate REJECTED the rewrite and left the negation
  // in place. A symbol base hid it (`(-x)^2 -> x^2` still worked).
  if (base.operator === 'Negate') return expCost + costFunction(base);
  if (isFunction(base, 'Multiply')) {